JavaScripts by Gscripts.net

Loupe.js and Loupe.png allows you to add a loupe (magnifier) to images on your webpages. It uses unobtrusive javascript to keep your code clean.

It works in all the major browsers - Mozilla Firefox 1.5+, Opera 9+, Safari and IE6+. On older browsers, it'll degrade and your visitors won't notice a thing.